Jiahe Cao, Yan Wang, Chuang Zhang, Guofeng Hu, Weihua Tang, Guosong Zeng, Daniela Gogova, Chee-Keong Tan
In this study, we employ first-principles calculations to explore the structural and electronic properties of monoclinic Al2O3/Ga2O3 superlattices with varied layer thickness and to perform a comparative analysis with (AlxGa1−x)2O3 alloys. Our investigation examines the lattice constants and electronic energy bandgaps of both the superlattice structures and alloys across different Al concentrations, shedding light on the intricate relationship between composition and electronic properties. The analysis on electronic properties reveals that as the number of Al2O3 monolayers in the Al2O3/Ga2O3 superlattice rises from 2 to 6 monolayers, the bandgap correspondingly expands from 5.29 to 6.43 eV. The band alignment between monoclinic Al2O3 and Ga2O3 exhibits a type-II band alignment. The conduction and valence band offsets between the bulk material and Al2O3/Ga2O3 superlattice varies with change in the number of Al2O3 monolayers. Our study gives a deeper insight into the properties of the Al2O3/Ga2O3 superlattice and suggests a solution to the Al-phase separation issue in (AlxGa1−x)2O3 alloys for advanced semiconductor device applications.
{"title":"Investigation on the structural and electronic property of monoclinic Al2O3/β-Ga2O3 superlattice with varying layer periods","authors":"Jiahe Cao, Yan Wang, Chuang Zhang, Guofeng Hu, Weihua Tang, Guosong Zeng, Daniela Gogova, Chee-Keong Tan","doi":"10.1063/5.0252684","DOIUrl":"https://doi.org/10.1063/5.0252684","url":null,"abstract":"In this study, we employ first-principles calculations to explore the structural and electronic properties of monoclinic Al2O3/Ga2O3 superlattices with varied layer thickness and to perform a comparative analysis with (AlxGa1−x)2O3 alloys. Our investigation examines the lattice constants and electronic energy bandgaps of both the superlattice structures and alloys across different Al concentrations, shedding light on the intricate relationship between composition and electronic properties. The analysis on electronic properties reveals that as the number of Al2O3 monolayers in the Al2O3/Ga2O3 superlattice rises from 2 to 6 monolayers, the bandgap correspondingly expands from 5.29 to 6.43 eV. The band alignment between monoclinic Al2O3 and Ga2O3 exhibits a type-II band alignment. The conduction and valence band offsets between the bulk material and Al2O3/Ga2O3 superlattice varies with change in the number of Al2O3 monolayers. Our study gives a deeper insight into the properties of the Al2O3/Ga2O3 superlattice and suggests a solution to the Al-phase separation issue in (AlxGa1−x)2O3 alloys for advanced semiconductor device applications.","PeriodicalId":8094,"journal":{"name":"Applied Physics Letters","volume":"61 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666387","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Two-dimensional gallium nitride (2D-GaN) has great potential in power electronics and optoelectronics. Heat dissipation is a critical issue for these applications of 2D-GaN. Previous studies have shown that higher-order phonon–phonon scattering has extremely strong effects on the lattice thermal conductivity (κlat) of 2D-GaN, with the fourth-order interatomic force constants (4th-IFCs) calculated using experienced atomic displacement in the finite difference method. In this work, it is found that the 4th-IFCs of 2D-GaN are quite sensitive to atomic displacement in the finite difference method. The effects of the four-phonon scattering can be severely overestimated with non-convergent 4th-IFCs. The κlat from three-phonon scattering is reduced by 65.6% due to four-phonon scattering. The reflection symmetry allows significantly more four-phonon processes than three-phonon processes. It was previously thought the electron–phonon interactions have significant effects on the κlat of two-dimensional materials. However, the effects of electron–phonon interactions on the κlat of both n-type and p-type 2D-GaN at high charge carrier concentrations can be neglected due to the few phonon–electron scattering channels and the relatively strong four-phonon scattering.
{"title":"Phonon thermal transport in two-dimensional gallium nitride: Role of higher-order phonon–phonon and phonon–electron scattering","authors":"Jianshi Sun, Xiangjun Liu, Yucheng Xiong, Yuhang Yao, Xiaolong Yang, Cheng Shao, Renzong Wang, Shouhang Li","doi":"10.1063/5.0256246","DOIUrl":"https://doi.org/10.1063/5.0256246","url":null,"abstract":"Two-dimensional gallium nitride (2D-GaN) has great potential in power electronics and optoelectronics. Heat dissipation is a critical issue for these applications of 2D-GaN. Previous studies have shown that higher-order phonon–phonon scattering has extremely strong effects on the lattice thermal conductivity (κlat) of 2D-GaN, with the fourth-order interatomic force constants (4th-IFCs) calculated using experienced atomic displacement in the finite difference method. In this work, it is found that the 4th-IFCs of 2D-GaN are quite sensitive to atomic displacement in the finite difference method. The effects of the four-phonon scattering can be severely overestimated with non-convergent 4th-IFCs. The κlat from three-phonon scattering is reduced by 65.6% due to four-phonon scattering. The reflection symmetry allows significantly more four-phonon processes than three-phonon processes. It was previously thought the electron–phonon interactions have significant effects on the κlat of two-dimensional materials. However, the effects of electron–phonon interactions on the κlat of both n-type and p-type 2D-GaN at high charge carrier concentrations can be neglected due to the few phonon–electron scattering channels and the relatively strong four-phonon scattering.","PeriodicalId":8094,"journal":{"name":"Applied Physics Letters","volume":"34 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666662","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dual-main-phase (DMP) magnets, a promising approach for the efficient utilization of high-abundance rare earth elements, exhibit enhanced coercivity compared to single-main-phase (SMP) magnets. This study demonstrates that a DMP magnet exhibits a 43 kA/m coercivity increase over an SMP magnet of equivalent composition. Microstructural characterization reveals two main-phase grains with distinct core–shell structures in the DMP magnet. Micromagnetic simulations indicate that the increased Nd content enhances the anisotropy field of the shells in Ce-rich grains, crucially contributing to the coercivity enhancement. Conversely, Nd2Fe14B grains do not significantly enhance coercivity. A micromagnetic model, constructed by substituting Nd2Fe14B grains with (Nd0.5Ce0.5)2Fe14B grains, demonstrates a slight coercivity increase compared to the DMP magnets. Moreover, retaining only the core–shell structure in grains near the end faces maintains higher coercivity than that of DMP magnets. Experimental results of DyCoCu grain boundary diffusion show a 406 kA/m coercivity increase in the DMP magnet, less than the 510 kA/m increase in the diffused SMP magnet. Although diffusion significantly increases the anisotropy field in the shell, the core region of the Ce-rich grains maintains a low anisotropy field, limiting magnetic property enhancement. These findings underscore the critical role of an optimized core–shell structure in enhancing coercivity for Ce-rich magnets, suggesting that the DMP method may not represent the most effective strategy.
{"title":"Effect of core–shell structure on magnetic properties and subsequent grain boundary diffusion in the Ce-rich dual main phase magnets","authors":"Chao Yang, Wei Li, Qiwen Zhu, Yuhua Hou, Zepeng Xu, Fengting Ni, Qing Zhou, Xiaowang Liu, Yuqi Xu, Huiyong Yang, Dunhui Wang, Youlin Huang","doi":"10.1063/5.0242694","DOIUrl":"https://doi.org/10.1063/5.0242694","url":null,"abstract":"Dual-main-phase (DMP) magnets, a promising approach for the efficient utilization of high-abundance rare earth elements, exhibit enhanced coercivity compared to single-main-phase (SMP) magnets. This study demonstrates that a DMP magnet exhibits a 43 kA/m coercivity increase over an SMP magnet of equivalent composition. Microstructural characterization reveals two main-phase grains with distinct core–shell structures in the DMP magnet. Micromagnetic simulations indicate that the increased Nd content enhances the anisotropy field of the shells in Ce-rich grains, crucially contributing to the coercivity enhancement. Conversely, Nd2Fe14B grains do not significantly enhance coercivity. A micromagnetic model, constructed by substituting Nd2Fe14B grains with (Nd0.5Ce0.5)2Fe14B grains, demonstrates a slight coercivity increase compared to the DMP magnets. Moreover, retaining only the core–shell structure in grains near the end faces maintains higher coercivity than that of DMP magnets. Experimental results of DyCoCu grain boundary diffusion show a 406 kA/m coercivity increase in the DMP magnet, less than the 510 kA/m increase in the diffused SMP magnet. Although diffusion significantly increases the anisotropy field in the shell, the core region of the Ce-rich grains maintains a low anisotropy field, limiting magnetic property enhancement. These findings underscore the critical role of an optimized core–shell structure in enhancing coercivity for Ce-rich magnets, suggesting that the DMP method may not represent the most effective strategy.","PeriodicalId":8094,"journal":{"name":"Applied Physics Letters","volume":"33 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666663","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
With both piezoelectric and ferromagnetic states, two-dimensional (2D) materials have garnered significant interest due to their immense potential in the field of spintronic devices. In this paper, the stability, electronic structure, piezoelectric properties, and magnetic characteristics of 2D piezoelectric ferromagnetic semiconductor MoXF (X = S, Se) monolayers were systematically investigated through first-principles calculations and Monte Carlo simulations. It is found that both MoSF and MoSeF are stable intrinsic ferromagnetic semiconductors and exhibit excellent out-of-plane piezoelectric coefficients (d31) of 1.05 and 1.40 pm/V, respectively, which surpass most 2D materials. They also possess out-of-plane magnetic anisotropy energy and high Curie temperatures (Tc, 227 and 210 K, respectively). In addition, biaxial strain has a significant effect on the piezoelectric properties and magnetic properties of MoSeF monolayers, which can enhance the application potential of the material. The findings suggest that MoXF monolayers hold tremendous potential for multifunctional semiconductor spintronic applications.
{"title":"Large out-of-plane piezoelectric response of ferromagnetic monolayer MoXF (X=S, Se): First principles predictions","authors":"Shiyu Xiao, Songli Dai, Furong Xu, Heng Wang, Zhigang Yu, Zean Tian","doi":"10.1063/5.0255746","DOIUrl":"https://doi.org/10.1063/5.0255746","url":null,"abstract":"With both piezoelectric and ferromagnetic states, two-dimensional (2D) materials have garnered significant interest due to their immense potential in the field of spintronic devices. In this paper, the stability, electronic structure, piezoelectric properties, and magnetic characteristics of 2D piezoelectric ferromagnetic semiconductor MoXF (X = S, Se) monolayers were systematically investigated through first-principles calculations and Monte Carlo simulations. It is found that both MoSF and MoSeF are stable intrinsic ferromagnetic semiconductors and exhibit excellent out-of-plane piezoelectric coefficients (d31) of 1.05 and 1.40 pm/V, respectively, which surpass most 2D materials. They also possess out-of-plane magnetic anisotropy energy and high Curie temperatures (Tc, 227 and 210 K, respectively). In addition, biaxial strain has a significant effect on the piezoelectric properties and magnetic properties of MoSeF monolayers, which can enhance the application potential of the material. The findings suggest that MoXF monolayers hold tremendous potential for multifunctional semiconductor spintronic applications.","PeriodicalId":8094,"journal":{"name":"Applied Physics Letters","volume":"24 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666666","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Passive solar heating and radiative cooling attracted lots of attention in global energy consumption reduction due to their unique electricity-free advantage. However, static single radiation cooling or solar heating would lead to over-cooling or over-heating in cold or hot weather, respectively. How to achieve effective self-adaptive thermoregulation is critical for dynamic thermal management. Hence, in this work, a self-adaptive thermoregulation strategy was designed by coupling latent heat storage or release with reversible solar heating and radiative cooling. A commercial memory alloy could realize self-adaptive thermoregulation at the critical temperature between radiative cooling with high solar reflectance R¯solar = 0.95 and thermal emittance ε¯LWIR = 0.93, and solar heating with high solar absorptance α¯solar = 0.92 and low thermal emittance ε¯IR = 0.08. High thermal conductive phase change material could further improve the thermoregulation performance with a latent heat of ∼136 J g−1, and thermal conductivity of 3.4 W m−1 K−1, resulting in a superior heating performance than the single solar heating (39.9 vs 36.9 °C) and superior cooling performance than the single radiative cooling (33.8 vs 35.5 °C). The maximum heating temperature increase could be 12.7 °C in the cold situation, and the temperature drop could be 8.3 °C in the hot situation. Energy consumption calculation showed that the designed sample could save 68%–90% of annual energy consumption compared with the common roof, indicating that coupling spectral regulation with the latent heat can greatly improve the self-adaptive thermoregulation performance and save the total energy consumption in thermal management.
{"title":"Reversible solar heating and radiative cooling coupled with latent heat for self-adaptive thermoregulation","authors":"Qin Ye, Na Guo, Meijie Chen","doi":"10.1063/5.0262028","DOIUrl":"https://doi.org/10.1063/5.0262028","url":null,"abstract":"Passive solar heating and radiative cooling attracted lots of attention in global energy consumption reduction due to their unique electricity-free advantage. However, static single radiation cooling or solar heating would lead to over-cooling or over-heating in cold or hot weather, respectively. How to achieve effective self-adaptive thermoregulation is critical for dynamic thermal management. Hence, in this work, a self-adaptive thermoregulation strategy was designed by coupling latent heat storage or release with reversible solar heating and radiative cooling. A commercial memory alloy could realize self-adaptive thermoregulation at the critical temperature between radiative cooling with high solar reflectance R¯solar = 0.95 and thermal emittance ε¯LWIR = 0.93, and solar heating with high solar absorptance α¯solar = 0.92 and low thermal emittance ε¯IR = 0.08. High thermal conductive phase change material could further improve the thermoregulation performance with a latent heat of ∼136 J g−1, and thermal conductivity of 3.4 W m−1 K−1, resulting in a superior heating performance than the single solar heating (39.9 vs 36.9 °C) and superior cooling performance than the single radiative cooling (33.8 vs 35.5 °C). The maximum heating temperature increase could be 12.7 °C in the cold situation, and the temperature drop could be 8.3 °C in the hot situation. Energy consumption calculation showed that the designed sample could save 68%–90% of annual energy consumption compared with the common roof, indicating that coupling spectral regulation with the latent heat can greatly improve the self-adaptive thermoregulation performance and save the total energy consumption in thermal management.","PeriodicalId":8094,"journal":{"name":"Applied Physics Letters","volume":"125 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666665","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yilin Cao, Yiyang Wen, Yongtao Yang, Fan Zhang, Wenjia Zhang, Jiangbing Du, Yang Zhang, Zhenping Wu, Jian Wu
Barium titanate (BaTiO3, BTO) thin films, with their exceptionally high Pockels coefficients, present a promising alternative to lithium niobate (LiNbO3, LN) for integrated photonic devices. BTO's compatibility with complementary metal–oxide–semiconductor (CMOS) technology further enhances its appeal, contingent on the development of low-temperature growth processes. This study investigates the impact of growth temperature on the electro-optic (EO) performance of BTO films, revealing a clear correlation between lower growth temperatures and reduced EO coefficients. Notably, BTO films grown at 400 °C maintain significant EO coefficients of approximately 51.6 pm/V. These findings underscore the potential of low-temperature grown BTO films for high-performance EO applications. By elucidating the relationship between growth temperature, crystallinity, and EO performance, this research provides critical guidelines for fabricating high-performing BTO films compatible with CMOS technology, facilitating the advancement of next-generation photonic devices.
{"title":"Low-temperature growth of epitaxial BaTiO3 thin films with significant electro-optic coefficients","authors":"Yilin Cao, Yiyang Wen, Yongtao Yang, Fan Zhang, Wenjia Zhang, Jiangbing Du, Yang Zhang, Zhenping Wu, Jian Wu","doi":"10.1063/5.0237644","DOIUrl":"https://doi.org/10.1063/5.0237644","url":null,"abstract":"Barium titanate (BaTiO3, BTO) thin films, with their exceptionally high Pockels coefficients, present a promising alternative to lithium niobate (LiNbO3, LN) for integrated photonic devices. BTO's compatibility with complementary metal–oxide–semiconductor (CMOS) technology further enhances its appeal, contingent on the development of low-temperature growth processes. This study investigates the impact of growth temperature on the electro-optic (EO) performance of BTO films, revealing a clear correlation between lower growth temperatures and reduced EO coefficients. Notably, BTO films grown at 400 °C maintain significant EO coefficients of approximately 51.6 pm/V. These findings underscore the potential of low-temperature grown BTO films for high-performance EO applications. By elucidating the relationship between growth temperature, crystallinity, and EO performance, this research provides critical guidelines for fabricating high-performing BTO films compatible with CMOS technology, facilitating the advancement of next-generation photonic devices.","PeriodicalId":8094,"journal":{"name":"Applied Physics Letters","volume":"91 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143660477","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xinjie Liu, Haiyan Hu, Xiao Wang, Rumeng Liu, Jun Yin, Lifeng Wang
Nanomechanical resonators crafted from two-dimensional materials exhibit heightened sensitivity to stress. The impact of tensile stress on resonators has received extensive attention. However, relatively little emphasis has been focused on the behavior of resonators under compression stresses, especially in the buckled state. This study explored the vibration of buckled graphite sheets under external excitation using experimental analysis, molecular dynamics (MD) simulations, and nonlinear isotropic plate model (NIPM). Notably, multiple peaks corresponding to the identical mode appeared in the spectrum. The additional peak distinct from the natural frequency arose from transition between two steady states of the film. Remarkably, the frequency of the peak corresponding to the transition exhibited greater sensitivity to external excitations and stress than the natural frequency of the resonator did. This phenomenon opens avenues for developing 2D resonant nanomechanical sensors with enhanced sensitivity, as well as bistable nanoelectromechanical resonators.
{"title":"Steady-state transition of buckled nano graphite sheets in vibration processes","authors":"Xinjie Liu, Haiyan Hu, Xiao Wang, Rumeng Liu, Jun Yin, Lifeng Wang","doi":"10.1063/5.0247821","DOIUrl":"https://doi.org/10.1063/5.0247821","url":null,"abstract":"Nanomechanical resonators crafted from two-dimensional materials exhibit heightened sensitivity to stress. The impact of tensile stress on resonators has received extensive attention. However, relatively little emphasis has been focused on the behavior of resonators under compression stresses, especially in the buckled state. This study explored the vibration of buckled graphite sheets under external excitation using experimental analysis, molecular dynamics (MD) simulations, and nonlinear isotropic plate model (NIPM). Notably, multiple peaks corresponding to the identical mode appeared in the spectrum. The additional peak distinct from the natural frequency arose from transition between two steady states of the film. Remarkably, the frequency of the peak corresponding to the transition exhibited greater sensitivity to external excitations and stress than the natural frequency of the resonator did. This phenomenon opens avenues for developing 2D resonant nanomechanical sensors with enhanced sensitivity, as well as bistable nanoelectromechanical resonators.","PeriodicalId":8094,"journal":{"name":"Applied Physics Letters","volume":"56 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143660478","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Compositing negative-thermal-expansion materials with Al is an effective strategy for obtaining light zero-thermal-expansion (ZTE) materials. However, the dimensional stability of those composites is not guaranteed due to the residual stress generated during fabrication and the microstructure instability of the matrix. Here, we studied the effects of heat treatments on the dimensional stability of ZTE Cu2P2O7/ZL101 composite (with 32 vol. % of ZL101) prepared using the pressure infiltration method. Compared with the as-cast case, after a certain heat treatment (water quenching after holding at 773 K for 1 h, then aging at 463 K for 8 h, and finally thermal-cold cycling between 463 and 77 K for three times), the dimensional stability was improved by a factor of 20 and the coefficient of thermal expansion (CTE) was highly reproducible in the subsequent temperature cycles test. The treated composite exhibits a CTE of −0.028 ppm/K at 240–305 K and a relatively high thermal conductivity of 29.5 W m−1 K−1 at room temperature, leading to a thermal distortion parameter well less than those of other ZTE materials. The improved dimensional stability and the CTE reproducibility can be attributed to the stabilization of matrix microstructure and the greatly relaxed residual stress as revealed by the analysis of 2θ-sin2ψ based on x-ray diffraction.
{"title":"Improved dimensional stability of zero-thermal-expansion Cu2P2O7/ZL101 composite by thermal treatment","authors":"Jiawei Zeng, Chenlong Wei, Guanyin Gao, Yanwei Ding, Yuxia Bai, Jianchao Lin, Buke Dong, Wenhai Song, Peng Tong, Yuping Sun","doi":"10.1063/5.0254207","DOIUrl":"https://doi.org/10.1063/5.0254207","url":null,"abstract":"Compositing negative-thermal-expansion materials with Al is an effective strategy for obtaining light zero-thermal-expansion (ZTE) materials. However, the dimensional stability of those composites is not guaranteed due to the residual stress generated during fabrication and the microstructure instability of the matrix. Here, we studied the effects of heat treatments on the dimensional stability of ZTE Cu2P2O7/ZL101 composite (with 32 vol. % of ZL101) prepared using the pressure infiltration method. Compared with the as-cast case, after a certain heat treatment (water quenching after holding at 773 K for 1 h, then aging at 463 K for 8 h, and finally thermal-cold cycling between 463 and 77 K for three times), the dimensional stability was improved by a factor of 20 and the coefficient of thermal expansion (CTE) was highly reproducible in the subsequent temperature cycles test. The treated composite exhibits a CTE of −0.028 ppm/K at 240–305 K and a relatively high thermal conductivity of 29.5 W m−1 K−1 at room temperature, leading to a thermal distortion parameter well less than those of other ZTE materials. The improved dimensional stability and the CTE reproducibility can be attributed to the stabilization of matrix microstructure and the greatly relaxed residual stress as revealed by the analysis of 2θ-sin2ψ based on x-ray diffraction.","PeriodicalId":8094,"journal":{"name":"Applied Physics Letters","volume":"59 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143660979","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Introducing ferroelectricity through symmetry breaking induces profound changes in the physical properties of a material. This study comprehensively tracks the ferroelectric polarization and phonon property changes resulting from interlayer sliding in a β-GaSe bilayer. The results indicate that sliding the upper layer of the bilayer induces charge transfer, causing polarization accompanied by periodic changes and reversal in non-polarized β-GaSe. Simultaneously, low-frequency optical phonons in polarized structures soften significantly, exhibiting a minimum or rapid decrease accompanied by the maximum value of in-plane polarization. Additionally, the sliding symmetry breaking has complex effects on phonon transport, causing intriguing changes in transport characteristics due to variations in group velocity and linewidth, which are closely related to ferroelectric polarization. This study reveals not only the polarization achieved in the β-GaSe bilayer through sliding-induced symmetry breaking but also its complex effects on phonons and profound physical changes, enriching our understanding of the associated condensed matter physics.
{"title":"Sliding-driven symmetry breaking induced ferroelectric polarization and phonon property modulation in a β -GaSe bilayer","authors":"Sihan Yan, Jia-Han Zhang, Bo Li, Lincong Shu, Shaohui Zhang, Songrui Wei, Chee-Keong Tan, Shan Li, Zeng Liu, Weihua Tang","doi":"10.1063/5.0257780","DOIUrl":"https://doi.org/10.1063/5.0257780","url":null,"abstract":"Introducing ferroelectricity through symmetry breaking induces profound changes in the physical properties of a material. This study comprehensively tracks the ferroelectric polarization and phonon property changes resulting from interlayer sliding in a β-GaSe bilayer. The results indicate that sliding the upper layer of the bilayer induces charge transfer, causing polarization accompanied by periodic changes and reversal in non-polarized β-GaSe. Simultaneously, low-frequency optical phonons in polarized structures soften significantly, exhibiting a minimum or rapid decrease accompanied by the maximum value of in-plane polarization. Additionally, the sliding symmetry breaking has complex effects on phonon transport, causing intriguing changes in transport characteristics due to variations in group velocity and linewidth, which are closely related to ferroelectric polarization. This study reveals not only the polarization achieved in the β-GaSe bilayer through sliding-induced symmetry breaking but also its complex effects on phonons and profound physical changes, enriching our understanding of the associated condensed matter physics.","PeriodicalId":8094,"journal":{"name":"Applied Physics Letters","volume":"16 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666664","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Barium titanate (BaTiO3, BTO) is considered to be a typical room temperature ferroelectric. We have fabricated fluorinated BTO (BTOF) polycrystalline ceramics by using NH4F as doping compounds, in which one fluorine substitutes for one oxygen. At room temperature, the BTOF samples retain the tetragonal ferroelectric crystal structure, but change toward cubic paraelectric phase with F increasing. However, the difference in charge between O2− and F− anions makes the Ti3+ arise in BTOT ceramics. The coexistence of ferroelectricity and ferromagnetism was observed in BTOF ceramics at room temperature by P–E loop and M–H loop. Moreover, these two ferroic orders originate from the Ti atoms. This work presents an alternative scheme for exploring multiferroic materials with large polarization and magnetization at room temperature, and we also expect preferable magnetoelectric coupling.
{"title":"Coexistence of ferroelectricity and ferromagnetism in fluorine-doped barium titanate at room temperature","authors":"Xu Zhang, Jing-Xue Wang","doi":"10.1063/5.0247984","DOIUrl":"https://doi.org/10.1063/5.0247984","url":null,"abstract":"Barium titanate (BaTiO3, BTO) is considered to be a typical room temperature ferroelectric. We have fabricated fluorinated BTO (BTOF) polycrystalline ceramics by using NH4F as doping compounds, in which one fluorine substitutes for one oxygen. At room temperature, the BTOF samples retain the tetragonal ferroelectric crystal structure, but change toward cubic paraelectric phase with F increasing. However, the difference in charge between O2− and F− anions makes the Ti3+ arise in BTOT ceramics. The coexistence of ferroelectricity and ferromagnetism was observed in BTOF ceramics at room temperature by P–E loop and M–H loop. Moreover, these two ferroic orders originate from the Ti atoms. This work presents an alternative scheme for exploring multiferroic materials with large polarization and magnetization at room temperature, and we also expect preferable magnetoelectric coupling.","PeriodicalId":8094,"journal":{"name":"Applied Physics Letters","volume":"41 1","pages":""},"PeriodicalIF":4.0,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143660485","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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